This invention relates to the hydrocarboxylation of olefins to form carboxylic acids. More specifically, this invention relates to the hydrocarboxylation of propylene with carbon monoxide and water in the liquid phase to produce isobutyric acid. The branched isomer of butyric acid is desired as it may be dehydrogenated to produce methacrylic acid.
Carboxylic acids have previously been synthesized from olefins, carbon monoxide and water in strong acids. However, temperatures in excess of 100.degree. C. and pressures in excess of 500 atmospheres were required to achieve satisfactory yields. Milder conditions could be used if the olefin and carbon monoxide were pre-reacted in a substantially anhydrous strong acid prior to the reaction with the required amount of water. Olefin polymerization is a competing reaction which lowers the selectivity of the hydrocarboxylation reaction to the desired carboxylic acid product.
U.S. Pat. No. 3,910,963 describes the hydrocarboxylation of olefins in sulfuric acid using co-catalysts comprising Group IIB metal ions. The reaction is greatly inhibited by excess water.
Hydroformylation catalysts comprising cobalt carbonyl and porphyrin promoter ligands are described in U.S.S.N. 104,644, filed Dec. 17, 1979, assigned to our common assignee.
Bregeault et al., "Metal Carbonyl Cations in Sulphuric Acid as Catalysts for Carboxylation Reactions of Hexanol and Hexene", Journal of Molecular Catalysis, 4 (1978) pages 225-229, discloses the carboxylation of 2 hexanol in concentrated sulfuric acid using a tetraprotonated phthalocyanineiron (Table 1 on page 227) to yield a mixture of carboxylic acids having from 5 to 8 carbon atoms.
U.S. Pat. No. 3,116,328 describes the preparation of hydrocarbon substitued thiuramdisulfide in the presence of a metal phthalocyanine catalyst at a pH of 7 to 12. U.S. Pat. No. 4,168,245 discloses the use of metal phthalocyanines for the treatment of petroleum distillates boiling in excess of 135.degree. C.
The rate of the strong acid catalyzed hydrocarboxylation reaction is relatively slow. Transition metal catalyzed hydrocarboxylation reactions conducted in organic solvent demonstrate increased rates of reaction, but lower the selectivity of the reaction such that the straight-chained carboxylic acid isomer is produced.